HOME ENTERTAINMENT 98

 BootLog.co.uk

HomeSoftwareArchiveTop TipsGlossaryOther Stuff

FEATURE

 

GETTING STARTED IN HOME CINEMA, PART ONE

 

COPY

Recreating the experience of watching a movie in a cinema, at home is not new idea. Rich people with big houses have been doing it for years, but now anyone can join in the fun. You don't need a lot of money either, or a vast amount of room, all it takes is a little determination and planning. The equipment is readily available and easy to use, the only real problem is deciding which way to go. That’s where we come in. This four-part series has been designed to guide you through the maze of technical jargon, marketing-speak, and plain old waffle, to help you make the right decisions.

 

Home cinema is no longer a luxury. If you have a reasonably recent TV, video and hi-fi, you could already have most of the components for a worthwhile system; or maybe you want to start from scratch. In either case home cinema can transform your viewing enjoyment. It puts you and your family in the best seats in the house, watching the movies you want to see, when you want to see them, what’s more the popcorn and fizzy drinks are a whole lot cheaper...

 

AN IMMEDIATE IMPROVEMENT

Even if the concept of full-blown home cinema holds no interest, you surely want to get the best picture and sound performance from your present set-up. If you have a stereo TV, VCR and satellite receiver -- or all three -- connected together only by aerial leads, then you are almost certainly missing out. Virtually all TV and video equipment built within the past eight to ten years have specialised SCART sockets on the back panels, carrying unadulterated audio and video signals. By connecting equipment together using a simple SCART to SCART leads, costing around five pounds,  large chunks of circuitry inside the TV are by-passed, eliminating noise and other undesirable by-products of signal processing, making a noticeable improvement to picture and sound quality.

 

If you have a stereo satellite receiver -- most models are these days -- and/or a NICAM VCR, but your television is a mono model, you don’t have to miss out on stereo sound, if you also have a hi-fi system. Most audio and video systems can be simply connected together using one or two inexpensive connecting leads. For the best effect place the hi-fi speakers a foot or two either side of the TV screen and connect the line-audio outputs from the VCR and satellite receiver to one of the auxiliary inputs on the hi-fi system amplifier. Most audio and video devices use simple push-fit phono (aka RCA or ‘cinch’) connectors; they’re conveniently colour-coded red and black (or white). It takes just a few minutes, and a little reorganisation, but the difference it makes can be quite remarkable. In the case of a NICAM VCR it means you will be able to watch TV programmes, and pre-recorded movies in stereo, without having to go to the expense of buying a new television. 

 

3D PHONIC AND OTHER TECHNOLOGIES

One of the major disadvantages of home cinema is the apparent need for lots of extra boxes and wires all over the place. Whilst it is true that you do need additional loudspeakers, to faithfully reproduce the acoustics of a large auditoria or theatre, research into the way we perceive sound, and recent advances in digital signal processing (DSP) mean it is now possible to create some quite impressive spatial and surround-sound effects, using just two speakers.

 

3D effects systems are now featured on a number of televisions and home cinema hi-fi systems. A variety of techniques are used, from simple stereo wide, which increases the apparent width of the stereo image, to replicating multi-channel cinema sound systems. The usual trick is to add in extra sounds to the original right and left stereo channels. A small portion of the signal is electronically delayed, for a few milliseconds, mimicking the low-level, almost subliminal sounds, that are reflected back to the listener from distant walls and the ceiling, creating a feeling of space. Most DSP systems work on the basic stereo soundtrack, or create pseudo stereo and surround effects from mono sources, some top-end models are able to extract surround-sound information hidden in the soundtrack. 

 

In all cases the basic laws of acoustics still apply and whilst is possible to create a sensation of sounds coming from somewhere other than the main loudspeakers, they cannot perform miracles and actually localise sounds behind the listening position. Most 3D systems also produce a fairly narrow and shallow ‘sweet spot’ where the effect will be most noticeable, and the shape of the room and proximity of walls can affect the shape of the soundstage. Nevertheless, if a full blown multi-channel surround-sound system is out of the question, or your living room  is on the small side,  they are worth investigating.

 

RECOMMENDED 3D TVs

 

JVC AV-21AX2EK, 21-inch NICAM TV £400 (25 and 29-inch TVs also available)

JVC have developed a hybrid Dolby Pro Logic system, called 3D Phonic, that processes and mixes movie surround sound information in with the stereo soundtrack. 3D Phonic TVs can also be upgraded to full multi-channel operation by adding extra amplifiers and speakers

 

SHARP 51DS05H, 21-inch NICAM TV, £350 (25-inch model also available)

Sharp use the SRS (sound retrieval system) to create a wide pseudo-surround soundfield. This works well with mono and stereo sources, and movie soundtracks with a lot of dynamic effects.

     

WHAT IS DOLBY PRO-LOGIC?

Once you’ve started your journey into home cinema you will quickly encounter the mighty and mysterious Dolby Pro-Logic or ‘DPL’. There’s a lot of confusion and mis-information around, so here are the plain facts. Dolby Pro Logic is four-channel surround-sound decoding and processing system, developed by Dolby Laboratories in the US. It should not to be confused with Dolby B or C noise processing, which is something quite different. DPL decoders are now fitted to a wide range of televisions and mini hi-fi systems, plus a handful of VCRs and satellite tuners. They’re also available as stand-alone components and upgrade kits, for existing home entertainment set-ups.

 

A DPL decoder’s job is to extract the four audio channels contained within the stereo soundtrack of several thousand movies made since the mid 1970s. The movies in question have what is known as a Dolby Stereo soundtrack; the first major film to be recorded in Dolby Stereo was Star Wars, released in 1972.

 

The four audio channels comprise the normal right and left stereo, the third is mainly used for dialogue and the fourth carries mostly sound effects. In a cinema the centre channel is used to focus the audience’s attention on the screen. This is important in a large movie theatre, especially for those seated away from the centre-line of the right and left channel speakers. The rear effects channel is used to create or enhance an atmosphere, by immersing the audience in sound -- the sound of falling rain or wind for example -- or to add impact to what’s happening on the screen, with loud explosions, rumbles. It is also used to emphasise movement, with sounds following the action, as it moves towards or away from the audience.  The four tracks are embedded into a normal two-channel stereo soundtrack using a phase shifting technique, which doesn’t affect normal stereo sound reproduction. The original intention was to allow cinema owners to upgrade to surround-sound, quickly and relatively cheaply, whilst the same movie prints could still be shown in older, less well-equipped cinemas.

 

Dolby Stereo was the catalyst for home cinema as we know it today. Movie fans in the US discovered that the extra channels were carried across when a movie was transferred on to tape or video disc, or shown on terrestrial and satellite television, (when broadcast in stereo). Demand for domestic decoders grew quickly during the early 1980s. First generation processors were only able to extract the rear surround channel, using ‘passive-matrix’ decoders. Soon after, more advanced four-channel decoders, based on movie theatre systems began to appear. The cost of ‘active-matrix’ or Dolby Pro-Logic decoders fell quickly, driven by demand and the rapid increase in the amount of material. By the late eighties a growing number of television programmes were produced with  Dolby Stereo soundtracks, though strictly speaking when Dolby Stereo is used on video or TV it should be referred to as ‘Dolby Surround’. 

 

The four channel outputs from a Dolby Pro Logic decoder are amplified and used to drive loudspeakers placed either side of, and below the television screen, (right, left and centre), the fourth surround channel is normally spit between two speakers placed behind the viewing position.

 

ADDING DOLBY PRO-LOGIC

The simplest route into home cinema is the so-called ‘one-box solution’ which refers to the fact that they’re usually packaged or sold in a single box. Inside there’s usually several boxes, and lots of wires...  DPL upgrade kits are generally the cheapest option, the processor and amplifiers are incorporated into the centre speaker enclosure, in one case a TV stand/console; a pair of rear surround speakers are normally supplied, some models include the front stereo speakers as well, others utilise the TV’s built-in speakers. Prices start at around £150 rising to more than £700 for the top-performers.

 

For those looking for a complete home entertainment package a DPL mini hi-fi system is hard to beat. Most packages include a CD player -- multi-disc autochangers are becoming more common -- twin cassette decks, AM/FM tuner amplifier, DPL decoder and DSP processor, plus a set of five speakers. Performance varies, generally in line with price, you can expect pay from around £400 upwards for a system that can do justice to both audio and video material, though you can pay more than £1000 for some top-end packages. 

 

DPL decoders turn up all sorts of places, including satellite receivers, column speakers and sub-woofers, even VCRs. In fact DPL video recorders make a lot of sense, particularly if space is at a premium. Akai were the first to market surround sound video recorders, way back in 1989, they currently have two models, costing £500 and £700 (VS-G2DPL & VS G2400DPL), they’ve been joined by the Sony SLV-AV100 (£750), a well-specified DPL AV amplifier, with a built-in VCR.

 

RECOMMENDED ONE-BOX SOLUTIONS

 

Philips MX900 DPL upgrade, £230

Everything is built into the centre speaker, it comes with rear speakers, just plug it into a NICAM VCR and TV and you’re in business

 

Aiwa NSX-AV75, mini DPL system, £400

Highly-featured, value for money system, bass effects are a little lightweight but performance is generally good and there’s plenty of toys to play with

 

Akai VS-G2DPL, DPL VCR, £500

In addition to being a top-notch home cinema VCR, this model has the DPL decoder and amplifiers built-in, simply add speakers.

 

DOLBY PRO LOGIC TVs

A television -- preferably a large screen model -- is the core component in any home cinema system, and a natural home for a Dolby Pro-Logic processor. The first models began to appear in 1994, though TVs with simpler, passive-matrix Dolby Surround decoders, went on sale in the UK some three years earlier. A DPL television is the ultimate one-box home cinema solution, though they do come with a few ifs and buts. The most obvious problem is the performance of the internal speakers.

 

Most TV cabinets are an acoustically-unfriendly environment. Cosmetic demands mean that the speakers on many DPL TVs are narrow elliptical types, mounted either side of the screen. They produce a thin, confined soundfield, which is the complete opposite of what you want in a surround sound system. Some set-makers try to beef up the sound with additional processing, spatial wide modes and a sub-woofer or two, but in the end separate outboard speakers are the only answer, though not all sets have external speaker connections.

 

Centre channel speakers are a real headache for DPL TV  manufacturers. Some mount them inside the cabinet, or rely on a ‘phantom’ centre channel, produced by the right and left speakers. Others fit the centre speaker into the console or stand, or leave it up to the owner to make their own arrangements. Rear channel speakers are not much better. They are often poor little things that splutter and gasp when driven hard, and the supplied connecting leads are always far too short.

 

The bottom line is that  the speakers on DPL TVs are usually their Achilles heel often having an adverse effect on performance. It pays to go for models where it is clear the manufacturers have taken a bit more time and trouble over the design of the acoustics, or the standard offerings can be easily replaced.

 

Trailing speaker cables are a problem for some but in the next few months several companies will be launching cordless RF speakers, using the newly ratified European standard 863MHz frequency band. Amongst them will be re-chargeable battery-powered models, with no trailing wires at all.

 

RECOMMENDED DPL TVs

 

HITACHI C2848TN, 28-inch NICAM DPL, £850

Dolby Pro Logic and 3D sound, a big TV that looks and sounds good; cordless IR speakers are available as an option

 

SHARP 59-CSD8H, 25-inch NICAM DPL, £650

Good value and above average performance; a built-in sub-woofer adds extra impact to action blockbuster movies

 

MITSUBISHI CT-28BW2BD, 28-inch widescreen NICAM DPL, £1000

A very attractively priced, and unusually well-equipped widescreen model; good bass and a lively, articulate DPL processor could make this one a classic

 

SEPARATE SYSTEMS

So far we have covered what can loosely be termed quick and easy solutions, but are they necessarily the best route into home cinema? Whilst some package systems and one-box outfits can produce quite pleasing results, they almost always involve some sort of compromise.

 

The answer is to put together a system using separate components of your own choosing, to meet your specific requirements. It needn’t be expensive either, in fact it can actually work out cheaper than a package system. You won’t be buying components you don’t want, or already have, moreover future upgrades will be a lot easier.

 

Separate home cinema AV systems tend to be based around the amplifier. Audio-visual or AV amplifiers come in a variety of configurations, the commonest being a combined multi-channel amplifier with an on-board DPL decoder. Most AV amplifiers usually include an assortment of pseudo surround and a DSP effects processor as well. The advantages of an AV amplifier lies in the integration of four or five channels of matched amplification, together in one box, simplified switching of source components and ease of use. Prices start at under £200, but you can expect to pay at least £300 for models with serious sonic capabilities.

 

AV receivers are an increasingly popular alternative. They’re AV amplifiers with a built-in AM/FM tuner. It’s a useful combination of technologies in a home entertainment system, reducing the box count still further. The latest models incorporate RDS (radio data system) decoders, often at little or no extra cost. RDS is a sort of radio teletext service, giving station and programme information, up to the minute traffic reports and news, presented on the front panel display. Quality AV receivers cost from around £300 upwards.

 

Of course it is possible to build a system around plain vanilla stereo amplifiers and a separate DPL decoder -- prices start at around £250 -- and this is the route many purists prefer, but apart from the added complexity it’s often a case of diminishing returns, when it comes to performance. The audio capabilities of video tape and disc fall somewhere between compact cassette and CD, moreover the rear effects and centre dialogue channels have a limited bandwidth. It is debatable whether there’s much point in using expensive high-end components to process relatively undemanding audio information in a basic DPL set-up, though the equation changes somewhat when it comes to higher-performance THX systems, and it will change once again, as we move towards digitally-encoded discrete multi-channel surround, that will be a feature of DVD. More about that too, in later issues. However, there is no question that it is worth paying a little extra for components that are designed specifically to do the job, which brings us to home cinema speakers.

 

We’ll be looking at AV speakers in considerable detail in the XXX issue but it’s fair to say that they are a breed apart from conventional hi-fi loudspeakers. Centre channel speakers are critically important to achieving a convincing surround sound effect; it’s vital that they match the characteristics of the right and left stereo speakers. All front speakers should be magnetically shielded, to avoid colour ‘staining’ on the TV screen. Rear speakers need to produce a widely dispersed soundfield, a variety of techniques have been developed to meet this need. Lastly, conventional speakers often lack the bass response needed for home cinema work, so it’s a good idea to budget for a sub-woofer as well.  

 

Speaker placement is something else we’ll be looking at in future issues. Suffice it to say that to achieve the best effect you may have to shift the furniture around a little, and be prepared to put up with a few extra wires and boxes, but then no-one said this was going to be easy.

 

Interconnections are a major bugbear for some people but it needn’t be a problem, if you take time to plan your installation beforehand. To give you an idea of what to expect we’ve drawn out some of the most commonly encountered configurations.  

 

BOX COPY 1

THE HAFLER EFFECT

It may surprise you to know that it’s possible to build a surround-sound decoder for around a pound. How? Well it all depends on the way Dolby Surround signals are processed, which in turn goes way back to something called the Hafler effect, on which the Dolby system is based. To cut a long story short, the rear effects and centre channels (S or surround and C or centre) are combined with the right (R) and left (L) stereo channels, to produce two outputs Rt (right total) and Lt (left total). The four signals exist in the same space, but are separated in phase. They can be extracted using a relatively simple technique whereby four speakers are wired together, so that they’re out of phase with one another (see diagram). All you need is a potentiometer (volume control), to set rear channel volume. It actually works, though some effects can be a bit messy, and the centre channel moves around a bit.

 

BOX COPY 2

JARGON BUSTER

 

Dolby Stereo

Four-channel surround-sound system used on movie soundtracks

 

Dolby Surround

Four-channel surround-sound system -- identical to Dolby Stereo -- but applicable to video and TV soundtracks

 

DPL

Dolby Pro Logic -- four channel active-matrix surround sound decoding system

 

DSP

Digital signal processing -- electronically generated spatial and pseudo surround effects

 

DVD

Digital Versatile (Video) Disc -- 12 cm optical disc system, capable of storing 4 hours or more of high quality video, and multiple digital soundtracks

 

NICAM

Near instantaneously companded audio multiplexing -- high quality digital stereo sound system used by UK terrestrial TV

 

SCART

Syndicat des Constructeurs d'Appareils Radio Recepteurs et

Televiseurs, 21-pin plug and socket system used on TVs and VCRs sold within the EC

 

THX

Technical specifications devised by Lucasfilm, applied to high quality home cinema equipment, cinema acoustics and movie to tape and disc transfers

 

---end---

Ó R. Maybury 1997 1011

 

[Home][Software][Archive][Top Tips][Glossary][Other Stuff]


Copyright (c) 2005 Rick Maybury Ltd.

admin@rickmaybury.com